In a robot used in various fields from an industrial robot to a humanoid robot, an actuator having a deceleration function is used to increase a torque of a joint.
Particularly, convergence of technology is underway for a robot technology being rapidly developed recently, as mechanisms of robot engineering used only for a conventional industrial purpose are being incorporated into other industrial areas. Examples are development and production of robots for cleaning homes, programming education, toys, entertainment, and so on.
In many robots which use decelerators attached to a motor to increase torque of a rotating shaft, a rotation angle detector such as an encoder or a resolver to detect a rotation angle of a motor is used.
When an encoder providing an absolute position to such a robot joint is added or a means enabling obtaining an absolute position is used, the joint, that is, the output shaft absolute position of the decelerator, can be controlled.
Various methods are used for a measurement of output shaft absolute position, such as performing homing every time to start driving thereof by using a relative position detector to the input shaft of the motor, storing the absolute position by using a status detector to the input shaft, using multi-revolution absolute position detector to the input shaft, detecting the absolute position by comparing position values of the two detectors by providing relative position detectors on the input shaft and the output shaft, respectively, deriving the output shaft absolute position by providing an absolute position detector on the output shaft and so on.
However, when the relative position detector is used for the input shaft, performing homing process at a time to start driving is difficult, and when there is a concern that a safety problem may occur in the process of implementing homing, the homing process cannot be implemented right away.
In addition, when multi-revolution absolute position detector is used, expensive parts are required thus increasing cost, when a reduction gear ratio is greater than the practicable number of revolutions of the absolute position detector, the multi-revolution absolute position detector cannot be used, and when the absolute position is stored by using a battery, at the time the battery is replaced, setting of the initial absolute position value and calibration of the absolute position value should be implemented.
Meanwhile, when the absolute positions are derived by using relative position detectors on each of the input shaft and the output shaft, derivation of the absolute positions is possible only when the conditions are met, wherein that relative position detector of each of the input shaft and the output shaft should be able to produce phase Z output, the reduction gear ratio should be an integer while the reduction gear ratio and the resolution of the output shaft position detector should be relative prime, and the input shaft position detector has a resolution higher than the output shaft position detector.
In addition, when a high-resolution absolute position detector is used on the output shaft, there is a drawback that not only cost is increased from the expensive parts, but also the size thereof becomes large. On the other hand, when a low-resolution absolute position detector was used on the output shaft to complement such a problem, there was a drawback that an accuracy of an initial position of the motor decreased as much as the resolution of the output shaft position detector.
Therefore, in a method proposed in the present disclosure, by providing the low-resolution absolute position detectors on each of the input shaft and output shaft, a high-resolution output shaft absolute position value can be derived from a relational expression defined based on each detected absolute position, already defined offset, and a reduction gear ratio.